1. Field of the Disclosure
The present disclosure relates generally to packet data recovery, and more particularly, to methods and apparatuses for recovering data using probe response frames or beacon frames received with errors.
2. Description of the Related Art
A wireless local area network (WLAN) device that is based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard relies on the correct reception of frames from neighboring devices in order to identify available networks. This reception is required prior to attempting to establish a connection to one of the available networks. This reception is also required to determine the location of the WLAN device, especially in areas where it is not possible to receive positioning signals from navigation satellites.
Interference caused by an increased deployment and usage of license-exempt industrial scientific and medical (ISM) band devices results in the incorrect reception of frames. Incorrect reception reduces the number of devices that are discovered within a fixed duration, resulting in either reduced reliability or increased power consumption.
Two approaches for scanning for networks are set forth in IEEE 802.11. In a first approach, referred to as passive scanning, the receiver is enabled for a fixed duration and picks up beacon frames that are broadcast by each network. The beacon frames are typically transmitted every 100 time units (TUs) or 102.4 ms. Thus, the receiver must remain enabled on each channel for a time that is slightly longer than 102.4 ms.
In a second approach, referred to as active scanning, a probe request is broadcast and then the receiver awaits a probe response that is unicast back to the device from each network. Active scanning reduces the amount of time that must be spent on each channel to approximately 5 ms. However, this amount of time is normally increased if other traffic is detected to allow for delayed or multiple responses.
Beacon frames are always broadcast, and therefore, automatic repeat request (ARQ) is not applied. This typically means that there is only a single opportunity to receive a beacon during the dwell time on each channel during passive scanning. It is not possible to request a retransmission of the packet if it is not successfully received.
Probe response frames are unicast to the device that transmitted the probe request, and therefore, they benefit from ARQ. If they are addressed to the scanning device, there will typically be up to seven opportunities to receive the frame. However, if the scanning device is attempting to receive a probe response addressed to a different device, there may be fewer retransmissions.
The IEEE 802.11 standard uses three main frame types: management, data, and control. Each frame type includes a medium access control (MAC) header, which is followed by a frame body, which is followed by a frame check sequence (FCS). The IEEE 802.11 standard specifies that frames received with an invalid FCS should be discarded. However, these partially received frames often contain useful information despite the errors.